DrugBuyers.Com: grapefruit

This was from a post a few weeks ago.

Whats Wrong with Grapefruit Juice?

Why should one avoid grapefruit when taking Valium or a cholesterol-reducing medication?

-- Anonymous

Today's Answer

(Published 03/28/2003)

Actually, grapefruit juice more than grapefruit seems to be the culprit it interferes with the absorption and metabolism of a number of drugs (although there is increasing concern that eating grapefruit might also lead to this effect).

Something in grapefruit juice no one knows what blocks the action of specific enzymes needed to absorb and break down drugs. These enzymes, found in the intestinal wall and liver, are called cytochrome P-450 3A4 and 1A2 (CYP3A4 and CYP1A2, for short). Several constituents of grapefruit juice have been implicated, including specific flavonoids and other phytochemicals called furanocoumarins. Concentration of these compounds varies from one batch of juice to another.

By inhibiting the action of these enzymes, grapefruit juice increases your bodys absorption of certain drugs, and also slows the process of breaking them down in the liver. Thus certain drugs affected by these enzymes stay in the body longer than normal. These include the calcium channel blockers used to treat high blood pressure, non-sedating antihistamines such as Hismanal (astemizole), certain tranquilizers including Valium (diazepam), Xanax (alprazolam), Halcion (triazolam), and others, a number of cholesterol-lowering drugs, including Lipitor (atorvastatin), Mevacor (lovastatin) and other statins, immunosuppressive drugs used to prevent rejection of transplanted organs and antiviral agents used to treat HIV/AIDS.

If you take any of these drugs with grapefruit juice, you may feel a difference. For example, with calcium channel blockers you might notice flushing, headache, an increased heart rate, or blood pressure which is lower than intended. With the tranquilizers, you may notice increased sedation. More dangerous side effects including kidney toxicity and increased susceptibility to infections could develop among those taking immunosuppressive drugs. Grapefruit juice can even enhance your response to caffeine, resulting in nervousness and over-stimulation.

Interestingly, grapefruit juice seems to be the only citrus juice to have this effect. If youve always taken your medication with grapefruit juice and never noticed any of the symptoms Ive mentioned, theres probably no reason to make a change, but it would be a good idea to tell your physician about your juice consumption. And if you have any concerns about whether grapefruit juice could be interfering with any medication you take, ask your physician or pharmacist about possible interactions.

Dr. Andrew weil

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